Hydraulic transformer

ABSTRACT

A bidirectional hydraulic transformer for transferring power to or from either one of two separate and isolated hydraulic control circuits without the transfer of any hydraulic fluid between the circuits. The transformer comprises two axial piston pump/motor devices, the rotors of which are interlocked so that they rotate together, one acting as a motor to drive the other as a pump and supply power to the pump connected circuit.

United States Patent Inventor Appl. No.

Filed Patented Assignee Herbert H. Kouns Camarillo, Calii'. 24,709

Apr. 1, 1970 Dec. 14, 1971 Abex Corporation New York, N.Y.

HYDRAULIC TRANSFORMER 14 Claims, 6 Drawing Figs.

US. Cl

Int. Cl Field of Search 417/271 F04b l/00 417/405, 271, 237

Primary Examiner- Robert M. Walker Attorney-Wood, Herron & Evans ABSTRACT: A bidirectional hydraulic transformer for transferring power to or from either one of two separate and isolated hydraulic control circuits without the transfer of any hydraulic fluid between the circuits. The transformer comprises two axial piston pump/motor devices, the rotors of which are interlocked so that they rotate together, one acting as a motor to drive the other as a pump and supply power to the pump connected circuit.

PATENTED [ED141971 SHEET 1 [IF 3 MwN 'PAT'ENTEIInEcmQn 3 27,45

sum 3 or 3 E:/E5' 1 INVENTOR.

%d/%w/l HYDRAULIC TRANSFORMER This invention relates to bidirectional hydraulic power transfer units and more particularly, to a hydraulic transfer unit for transferring hydraulic power at the same pressures and in either direction between two separate and isolated hydraulic control systems.

Hydraulic transfer units or so-called transformers are now commonly used in aircraft to transfer power from one hydraulic control circuit to another separate and isolated control circuit while maintaining the integrity or isolation of both systems. In this type of application, a transfer unit is interconnected between the two hydraulic systems or circuits and operates to transfer power from either one to the other. It comprises two axial piston pump/motor units, the rotors of which are mechanically interlocked. Either unit is capable of operating as either a pump or a motor depending upon whether the power input in the form of fluid flow to the pressure port is less than or greater than the torque restraining movement of its rotor. In the aircraft applications, the pressure port of one pump/motor unit is connected to one control system or circuit, as for example, the main hydraulic control system of the aircraft, and the pressure port of the other pump/motor unit is connected to a second hydraulic control system, as for example, the auxiliary aircraft control circuit. Most larger aircraft today utilize a main control circuit to control rudders and elevators and an auxiliary control circuit to control landing gear, wing flaps, etc. If a hydraulic transfer unit or transformer is thus connected between the two systems, the unit is operable to transfer hydraulic power from one system to the other if the power in the other falls below a preset value. As an example,,if the power level in the main control circuit should fall from operating value of 3,000 p.s.i., while the pressure level in the auxiliary control circuit remains at 3,000 p.s.i., the pump/motor unit which is connected to the auxiliary control circuit is automatically operable as a motor to drive the other unit as a pump and thereby increase the pressure in the other or main circuit. Alternatively, if the pressure in the auxiliary circuit should fall below the operating level of 3,000 p.s.i. while the pressure in the main control circuit remains at 3,000 p.s.i., the unit connected to the main control circuit is operative as a motor to drive the unit connected to the auxiliary circuit as a pump and thereby increase the fluid pressure in the auxiliary circuit.

One common limitation of bidirectional hydraulic transformers occurs because of the inherent power losses in the transformer. As a result, a 3,000 p.s.i. pressure input to one motor can only generate something less than 3,000 p.s.i. pressure on the interlocked pump assuming the units are identical in capacity. Consequently, if the capacity of the two pump/motor units is identical, the hydraulic transformer cannot be used bidirectionally to maintain the pressure in the two circuits at the same level.

It has therefore been a primary objective of this invention to provide a hydraulic transformer which is capable of operating bidirectionally to maintain equal pressure levels in two isolated hydraulic circuits. This objective has been accomplished and this invention is partially predicated upon the concept of bypassing to a low pressure line a portion of the flow from either unit when it operates as a pump. Thereby, the pressure of the fluid flow from the unit acting as a pump is increased, preferably to the same level as the pressure level of the motor operating to drive the pump.

One way of increasing a pump pressure is to decrease the pump capacity (flow) while maintaining a fixed torque input to drive the pump. With a given torque input pressure increases approximately inversely to flow so that by decreasing the flow the pressure may be increased. This principle is utilized in enabling the hydraulic transformer of this invention to transfer hydraulic fluid bidirectionally between two isolated circuits at the same pressure.

The hydraulic transformer of this invention comprises two mechanically interlocked axial piston pump/motor devices. The port plate of each device has a high pressure port and a low pressure port as well as a third port located between the two for bypassing a portion of the flow to a low pressure line when the unit is operable as a pump. When the unit is operable as a motor, the third port is in effect closed by connecting it to the high pressure port of the same unit. As a result, the output flow and torque of the unit as a motor is normal but the output flow of the unit as a pump is reduced while the torque remains the same. In effect, the transfer unit then operates as a small pump driven by a larger motor with the small" pump then generating a higher pressure than would be the case if the two units were of the same capacity. By properly selecting the size and location of the third port, the transfer unit may be operated so as to generate the same pressure on the pump outlet as is used to drive the motor inlet of the device. Thereby, the transfer unit may be used bidirectionally to assist in maintaining the same pressure level in two physically isolated hydraulic circuits or control systems without the transfer of any hydraulic fluid between the two.

One additional advantage which accrues from the use of the invention of this application to hydraulic transformers is to increase the breakaway pressure level of the pump/motor unit as a pump. As an example, where without the application of this invention to the transformer the pressure differential required between the two systems to initiate operation of the transformer might be 300 p.s.i., the breakaway pressure level may be reduced to as little as one-third of this differential, i.e., I00 p.s.i. Thereby, by the application of this invention to the hydraulic transformer the'pressure level in the two systems may be maintained within a much closer range, i.e., the differential required to effect breakaway of the unit as a pump is reduced.

These and other objects of this invention will be more readily apparent from the following description of the drawings in which:

FIG. 1 is a cross-sectional view through a hydraulic transformer used in the practice of this invention.

FIG. 2 is a diagrammatic cross-sectional view of the transformer of FIG. 1.

FIG. 3 is a diagrammatic illustration of a hydraulic transfonner and two isolated hydraulic control circuits interconnected by the transformer.

FIG. 4 is a diagrammatic illustration similar to FIG. 3 but illustrating the circuits in a condition in which one pump/motor unit of the transformer is acting as a pump and the other as a motor.

FIG. 5 is a diagrammatic illustration of a second embodiment of one pump/motor unit control circuit incorporating a second modification of the invention of this application.

FIG. 6 is a view similar to FIG. 5 but illustrating the circuit in the pumping mode of operation.

Referring now in greater detail to the drawings and particularly to FIGS. 1 and 2, the numeral 1 designates a so-called hydraulic transformer. This transformer consists of two hydraulic axial piston pump/motor units 2 and 3 contained within a unitary housing 4 and mechanically interconnected by a tie bar or drive shaft 5. Each of the pump/motor units 2 and 3 is operable either as a pump or a motor depending upon whether its rotor is driven by an auxiliary source of input torque or is operable to drive the rotor and connected output shaft by an input source of pressure of greater force than the restraining torque on the rotor and connected shaft 5.

The hydraulic transformer except for the porting of the port or valve plate 6 of each unit 2 and 3 is a conventional hydraulic transformer available commercially from the Aerospace Division of Abex Corporation located in Oxnard, Calif. It therefore ishiot described in great detail herein. For purposes though of facilitating understanding of the operation of the transformer and of the invention of this application, one pump/motor unit 2 will be described generally and to that end its operating elements are illustrated diagrammatically in FIG. 2. Since both pump/motor units are identical including their port or valve plates 6, only one is described in detail herein. Similar components of the other pump/motor unit have been given identical numerical designations followed by the sufiix a" in order to distinguish the two.

The pump/motor unit 2 includes the outer casing 4 of multiple part construction suitably assembled as by tie bolts (not shown). The casing 4 includes a port or valve plate 6 which is formed with a high pressure port 9, a low pressure port 10 and a third port 1 1 (see FIGS. 3-5).

A generally annular-shaped cylinder block or barrel 12 is disposed within the outer casing 4 and is adapted to be rotated therein by a drive shaft 13. To that end, the shaft 13 is formed with external splines 14 at the end which are engageable with internal splines formed on a sleeve 15. The sleeve 15 is in turn axially disposed withina longitudinally extending central bore 16 formed in the cylinder barrel 12. The sleeve is connected to drive the cylinder barrel 12 through a splined connection 18 and is preferably formed with a web 19 extending across the outer end thereof. A spring 20 is interposed between the web 19 and the end of the shaft 13. The sleeve 15 also includes a radially extending flange 21 which is seated within an annular recess formed within one face of the cylinder barrel 12 to prevent axial movement of the cylinder barrel 12 in one direction. The opposite face of the cylinder barrel 12 is engageable with and slidable on the inner face of the plate 6 at the plane indicated by the reference numeral 22 so that the cylinder barrel is maintained in a fixed axial position within the outer casing.

The cylinder barrel 12 is formed with a plurality of axially extending cylinders or bores 24 disposed in an annular array. These bores 24 form chambers which are placed in alternate communication with the high pressure port 9 and the low pressure port 10 during rotation of the cylinder barrel 12.

Cylinder pistons 25 are slidable within the bores 24 and are adapted to be reciprocated back and forth therein by fluid under pressure entering them from the inlet port 9 and by a swash plate mechanism indicated generally by the reference numeral 26. Each of the pistons 25 is rounded cylindrically as indicated by the reference numeral 28, at the end which projects from the cylinder barrel 12. The rounded ends of the pistons 25 are received within complementary shaped recesses formed in slippers or shoes 29, thus affording a knuckle connection between the pistons 25 and the shoes 29. The shoes 29 are in turn slidable along the surface of a swash plate 30 in the course of the rotation of the cylinder barrel 12 and the pistons 25 carried therein. The swash plate 30 is suitably affixed within the housing 4 by a keeper ring 31. The shoes 29 are maintained in engagement with the swash plate 30 by a retainer assembly 32 which includes a ring 33 engageable with a radial flange 34 formed integrally on the shoes 29.

Both pump/motor units 2, 3 are fixed displacement units because of the swash plates 30, 30a being fixedly mounted at a predetermined angle relative to the axis of the units.

At their inner ends, the drive shafts 13, 13a of the two units are mechanically interconnected by the connecting shaft 5. The shaft 5 is splined at,both ends and is receivable within splined bores 36, 36a of the drive shafts 13, 13a so that it mechanically connects and interlocks them in driving relationship.

At its inner end, the drive shaft 13 is supported for rotation in the housing 4 by ball bearing raceway 38. A fluid seal 39 and 40 is mounted between the drive shaft and the bearing 38 so as to prevent fluid leakage from the pump to the motor or vice versa. Consequently, the drive fluid of the two systems may be different and one could even be a gas while the other is a liquid.

To maintain the integrity of the pump fluid system from the motor fluid system, the chamber 41 between the two units may be connected to a fluid drain through a port 42 of the unit 2 or a port 42a of the other unit 3. The ports and thus the chamber 41 are connected to drain through a passageway 43, 43a. As illustrated in the drawing, a plug 44, 44a is mounted within each of the passageways 43, 43a.

The interior of the pump/motor unit 2 within the housing 4 is connected to a drain port 46 via a passageway 47. As illustrated in the drawings, this port 46 is shown as being blocked by a plug 48.

The axial piston pump/motor units heretofore described are conventional except for the port plates 6, 6a as is explained more fully hereinafter. When the hydraulic pump/motor unit is operated as a pump, rotational energy from the connecting shaft 5 is supplied to the barrel which causes the barrel to be rotated. When the unit is operated as a motor, the barrel supplies rotational energy to the connecting shaft 5. The barrel is journaled by bearings 8 for rotation in the housing 4.

The cylinder barrel 12 is provided with a plurality of cylinders or piston chambers 24. These cylinders are parallel to the axis of the shaft 13 and are uniformly spaced around the axis. A sausage shaped cylinder port 17 extends from the inner end of each cylinder 24 to the end surface plane 22 of the cylinder barrel. One of these sausage-shaped ports 17 is superimposed in dotted lines upon each of the port plates 6, 6a in FIGS. 3-6.

In FIG. 2 of the drawings, the piston 24 at the top of the view is in the bottom dead center position BDC and the piston at the bottom of the view is in the top dead center TDC position. In this figure, a dot-dash line BDC-TDC is shown which extends between the centers of the bottom and top dead center positions. This line BDC-TDC is superimposed upon FIG. 3 to indicate the bottom and top dead center positions of the pistons with respect to the various ports in the port plate 6.

Between the adjacent ends of the high pressure port 9 and low pressure port 10 on the left side of the plate as viewed in FIG. 3, there is a sealing area 50. There is another sealing area 51 between the right end of the high pressure port 9 and the third port 11. A third sealing area 52 is located between the third port 11 and the right side of the low pressure port 10 as viewed in this figure. The BDC end of the line BDC-TDC extends across sealing area 52, while the TDC end extends across sealing area 50, so that neither intersects the ports 9, 10 or 11. The angular dimension A of each of these separation areas 50, 51 and 52 is slightly greater than the angular dimension B of the sausage-shaped port 17 in the end of each cylinder.

As shown schematically in FIGS. 3 and 4, the third port 11 is connected to a fluid pressure operated valve 62 of the shifting spool type. This valve 62 has a body 63 which contains a bore 64. A spool 66 is slidable in the bore 64 and this spool 66 has three spaced lands 67, 68 and 69 which are separated by two circumferential grooves 70, 71. A coil spring 73 biases the spool toward the right as viewed in FIGS. 3 and 4. The spool is illustrated in this position on the right-hand side of FIG. 4.

The third port 11 of the port plate is connected by a line 75 to a port 76 in the body 63 of the valve 62. This port 76 is open to the flow of fluid from the high pressure port 9 of the port plate through lines 77, 78 and port 79 when the spool 66 is in its leftwardmost position as illustrated in FIG. 3. The spool assumes this position when the pressure from the high pressure port 9 in the end chamber 80 overcomes the biasing force of the spring 73. The chamber 80 is connected to the high pressure port 9 through fluid line 77, a line 81 and port 82. When the force of the spring 73 overcomes the fluid force in the chamber 80, the spool 66 moves to the right to the (pump mode) position illustrated in FIG. 4 in which the port 76 is opened to a port 83 through the groove 71. In this position of the spool, the third port 11 is connected by the line 75 and a line 84 to the low pressure port 10 of the port plate 6.

In operation, the high pressure port 9 of the pump/motor unit 2 is connected to a first fluid control circuit including a fluid line by a line 91. The low pressure port 10 is connected to a source of fluid as for example a tank or reservoir 92 by a line 93. In the same manner, the high pressure port 9a of the pump/motor unit 3 is connected to another control circuit or system having a line 94 by a line 95. The low pressure port 10a of the pump/motor unit 3 is connected to a source of fluid or reservoir 97 by a line 96.

The two circuits or systems as represented by the lines 90 and 94 are completely independent and separate as well as being physically isolated. The only common link or connection between the two is through the transformer 1. Consequently, power or torque transfer is possible between the two systems or circuits but fluid transfer does not occur. In actuality, the line 90 might be a fluid line of a main control circuit of an aircraft and the line 94 might be a fluid line of an auxiliary control circuit of an aircraft. Most larger aircraft maintain two such separate systems, both of which are maintained in a pressurized condition during flight. The main circuit commonly controls the rudder and elevators of the aircraft while the auxiliary circuit controls landing gear and other auxiliary systems.

Commonly, and so long as both the main and auxiliary control circuits and the lines 90, 94 remain at full pressure, as an example at 3,000 p.s.i., neither unit 2 or 3 is operative to drive the other. They remain stalled with no power transfer between the two because the torque exerted by one in an attempt to drive the other is exactly matched by the torque of the other or second attempting to drive the first. This condition is depicted in FIG. 3 in which both units are acting as stalled motors at full pressure attempting to drive the other but incapable of generating sufficient torque on the rotor to overcome the restraint imposed by the interconnecting shaft 35.

Referring now to FIG. 3, both the main and auxiliary control circuits are depicted as being at full pressure, 3,000 p.s.i. in the example. In this condition, both units 2 and 3 act in effect as a motor and both valves 62, 620 are in their leftwardmost position. The valves are held in this position so long as the pressure in the high pressure ports 9, 91: remains sufficiently high to overcome the bias of the springs 73, 73a. This fluid pressure is transmitted to the chamber 80 via the fluid lines 77, 81.

Should the pressure in either the main or auxiliary circuit and thus in lines 90 or 94 fall to a value such that the bias of the spring 73 is capable of overcoming the counteracting pressure in chamber 80, the spool of the valve associated with that unit 2 or 3 will move to the right as illustrated in the diagrammatic illustration of the unit 2 depicted in FIG. 4. As the spool 62 of the unit 2 moves to the right upon a drop in the pressure chamber 80, the port 76 of the valve is connected to the port 83 via the spool groove 71. This results in the third port 11 of the unit being connected to the low pressure port through the valve 62 and simultaneously being disconnected from the high pressure port 9 by the land 68 moving over and blocking the port 79. A trap pressure relief valve 87 is connected between lines 75, 77 to release the high pressure fluid that is trapped within the bore 64 after the land 68 blocks port 76 and prior to opening of port 76 to the low pressure port 83.

When the pressure in the line 90 drops to a value at which the torque of the motor 3 is capable of overcoming the restraining torque imposed by the other unit 2 through the connecting shaft 5, the pump/motor unit 3 will act in its motor mode to drive the unit 2 in its pump mode. When operated as a pump, the unit 2 increases the pressure in the line 90 of the main circuit back to its original value.

As shown schematically in F IG. 4, when the unit 2 is driven as a pump, its rotor is caused to rotate in a counterclockwise direction. This direction is indicated by the arrow 98 which shows the port 17 of the rotor in dashed lines as rotating in the counterclockwise direction over the port plate 6. As here depicted (in the left side of FIG. 4), the port 17 is at its bottom dead center position in which the line at BDC bisects the port 17. When the port 17 is in this bottom dead center position, it and consequently its cylinder 24 are sealed from both ports 10 and 11 and the cylinder 24 is in the position of maximum cylinder displacement, i.e., its volumetric capacity is the greatest. As the cylinder 24 moves past the point of maximum cylinder volume, i.e., past bottom dead center, its volume in which the fluid is contained begins to diminish but the fluid contained in that volume is not released until the cylinder comes into communication with the third port 11. Since the third port 11 is now connected via the line 75 and valve 62 to the low pressure port 10, a portion of the fluid contained in the diminishing volume cylinder 24 is dumped back to the suction or low pressure port 10. The cylinder 24 then moves from communication with the port 11 over the sealing section 51 of the port plate during which the pressure on the fluid in the cylinder is increased untilthe leading edge 17b of the port 17 begins to overlap the edge 9b of the high pressure outlet port 9. Fluid is displaced from the cylinder 24 as the volume thereof continues to diminish while the cylinder moves across the pressure port or outlet port 9 toward the top dead center position TDC. When the cylinder is in the top dead center position its volumetric capacity is at its minimum and its contents are under high pressure. After passing top dead center position and while continuing to rotate in the counterclockwise direction, the volumetric capacity of the cylinder increases as the cylinder travels over the low pressure suction port 10. In so doing and as the volumetric capacity increases, the cylinder fills with low pressure fluid until the cylinder reaches the bottom dead center position of maximum cylinder displacement. This pumping action continues so long as and until the pressure in the main hydraulic control system and line reaches a value at which the pump stalls out because the torque imparted from the other unit 3 acting through the shaft 5 is restrained by the pressure in the line 90. Preferably this stall condition will be reached when the pressure in the main line 90 exactly matches the pressure in the auxiliary line 94.

When this condition occurs and the transformer 1 stalls, the pressure acting in the chamber 80 causes the piston 66 to be moved to the left against the spring bias, thereby closing the port 76 to the port 83 and disconnecting the third port 11 from the low pressure port 10. This results in the third port 11 being connected to the high pressure port 9 via the port 79 and the groove 70.

When the unit 3 is acting as a motor to drive the unit 2 as a pump, the third port 11a is connected to the high pressure port 9a so that it in effect forms a continuation of the high pressure port 9a. This condition makes the angular distance or length C of the high pressure port equal to the angular distance D of the low pressure port [00.

Referring now to the right side of FIG. 4, the unit 3 is depicted in its mode of operation as a motor operable to drive the unit 2 as a pump. The port 17a is shown as in its top dead center position in which it is sealed from both the low pressure port 10a and the high pressure port 9a. In this position of the port 12a it covers the sealing area 50a and bisects the top dead center position. The cylinder 24a then is in the position of minimum volumetric capacity. As the rotor rotates in a clockwise direction, the cylinder 24a moves from its position of minimum volumetric capacity over the pressure port 9a. Liquid at 3,000 p.s.i. in this example is then supplied to the port 9a. This liquid under pressure causes the barrel to rotate in the direction of expanding cylinder volume or clockwise. As the cylinder volume expands, the cylinder fills with fluid under high pressure until the port 17a passes over and out of communication with the third port 11a. The port lla then acts as a continuation of the high pressure port 9a. The port then passes over the sealing area 52a and into communication with the low pressure port 10a. As the port passes over its bottom dead center position BDC, it reaches its position of maximum volumetric capacity in which the chamber is full of high pressure fluid. Continuing its rotation in the clockwise direction, the high pressure fluid is then squeezed out of the chamber 24a as the port 17a passes over the port 10a.

When the unit 2 or 3 is operated as a pump, the third port 11 is automatically connected to the low pressure port 10 via the valve 62. Consequently, the high pressure port 9 is automatically foreshortened. In effect, this reduces the volume of flow from the unit when acting as a pump even though the torque input to it from the other unit remains normal. When this occurs, it automatically results in a pressure increase of fluid being pumped from the unit. Assuming the two units 2 and 3 to be of the same volumetric capacity, the third port and valving arrangement heretofore described results in that unit which is acting as a motor being operable to drive a pump of a lesser flow capacity. Consequently, the unit acting as a motor may drive the other unit as a pump until the two pressures are exactly equal. In the absence of this third port and valve arrangement, power losses resulting from inefi'iciency of the two units would preclude two units of the same capacity from operating at the same pressures.

Otherwise expressed, a fixed displacement hydraulic motor 3 of one capacity is not capable of driving another fixed displacement pump 2 of the same capacity at the same pressure as the pressure being used to drive the pump because of power losses and inefficiency of the two units. However, the invention of this application automatically lowers the flow capacity or displacement of that unit which is acting as a pump while maintaining the capacity of the motor at its normal value. The torque output of that unit which is acting as a pump remains the same or normal, i.e., equal to the torque input less the inefficiency of the two units so that the pressure of the pump unit is automatically increased. As a result, the transfon-ner may be interconnected to two circuits of the same operating pressure and may operate to maintain the pressure in either circuit at the same value. In the absence of this invention, a transformer consisting of two pump/motor units of the same capacity could not operate to maintain the two at the same pressure level.

Another advantage of this invention is that by reducing the volumetric capacity of the pump/motor unit when it acts as a pump, the breakaway pressure of the unit is thereby reduced. Consequently, the differential pressure required between the two circuits to cause the first circuit to drive its pump/motor unit as a motor and overcome the torque of the other unit acting as a pump is substantially reduced, often by as much or more than 50 percent. In one application, the pressure breakaway differential required to initiate operation of the transformer was reduced from 300 p.s.i. to 100 psi.

Referring now to FIGS. and 6 there is illustrated a second embodiment of a valving arrangement for connecting the third port 11 of either the pump/motor unit 2 or 3 to the high pressure port 9 in the motoring mode of operation and to a low pressure port in the pumping mode of operation. In these figures, the transformer unit 1 is identical to the transformer of FIGS. 14 so that similar numerals have been given to identical components to designate the same parts. The unit depicted in FIG. 5 has been numerically designated with the same numbers used to designate the pump/motor unit 2 in FIGS. 3 and 4 but it could just as well be the pump/motor unit 3.

In the modification shown in FIGS. 5 and 6, the third port 11 is connected in the motoring mode to the high pressure port 9 via a line 101, a spool valve 102 and a fluid line 103. It is connected to the low pressure port 10in the pumping mode via the line 101, the valve 102 and a line 104.

The spool valve 102 comprises a cylinder 105 within which the spool 106 is slidable. The spool has two lands 107 and 108 separated by a groove 109. One end chamber 110 of the cylinder is connected to the third port 11 of the motor pump unit by the fluid line 101 and a line 112. The opposite end chamber 113 is connected to the third port 11 via a fluid line 114, a check valve 115 and the line 101.

In the motoring mode of operation as depicted in FIG. 5, the third port 11 is connected to the high pressure port 9 via the line 101, the check valve 115, lines 116, 117, port 118, groove 109, port 119 and line 103. In this position of the valve 102, the check valve 115 opens and allows fluid to flow from the line 116 into the line 101 if the pressure in the third port 11 is less than the pressure in the high pressure port 9.

In the pumping mode of the operation of the pump/motor unit, the port 11 is connected to a low pressure or case pressure line 120. As explained more fully hereinafter, this low pressure line has a one-way check valve 121 in it which allows only one-way flow to the tank or low pressure side 125 and precludes flow in the opposite direction. The connection of the port 11 to the low pressure line 120 is via the lines 101, 1 12, port 122, and chamber 1 10 to the port 123.

The fluid circuit including the valve 102 depicted in FIGS. 5 and 6 is operable in the same manner as the circuit illustrated in FIGS. 2, 3 and 4. Specifically, it connects the third port 11 to either the high pressure port 9 or a low pressure or case pressure line 120 depending upon whether the unit operates as either a motor or a pump. The only difference between the circuit depicted in FIGS. 5 and 6 and that depicted in FIGS. 3 and 4 is that the valve 102 is operable to automatically move to position the valve spool 106 at startup depending upon the direction of rotation of the unit. It does not rely upon spring pressure to maintain the valve spool in a biased position as a motor.

Assuming that the valve 102 is in the position illustrated in FIG. 5 and the pressure in the line should fall to a value at which the torque of the other unit is capable of driving the unit here depicted as a pump (which we shall assume is the unit 2), the rotor will automatically start to rotate in the counterclockwise direction. As a result, fluid contained within the cylinder 24 is at its maximum when the cylinder reaches the position at which its port 17 is in the position illustrated in phantom in FIG. 6. This is the bottom dead center position. Upon continued rotation in the counterclockwise direction and as the leading edge 17b of the port 17 breaks over into communication with the third port 11, the swash plate causes the piston to move inwardly, thereby decreasing the volume of the cylinder 24. This forces fluid out through the third port 1 1 and line 101 into the chamber at the right end of the spool 106. The spool 106 then moves to the left as viewed in FIG. 6, thereby forcing fluid from the chamber 113 through the check valve 115. After the spool has moved fully to the left, the port 11 is in communication with the low pressure line and is operable to dump fluid at low pressure to the low pressure line through check valve 121. The volumetric capacity of the unit is then in this pump mode of operation less than it is in the motor mode of operation.

Assuming now that the pressure in the other unit should fall to a value at which the unit depicted in FIGS. 5 and 6 operates as a motor and the valve is in the pumping position illustrated in FIG. 6, it will then automatically move to the motor mode position depicted in FIG. 5. This occurs as a result of the startup of rotation of the rotor in the clockwise direction. When rotated in this direction, as the port 17 moves out of communication with the third port 11, the volumetric capacity of the cylinder 24 associated with that port 17 is increasing. Fluid is therefore required to fill that chamber. This fluid is pulled from the chamber 110 at the right end of the spool 106 into the port 11 thereby moving the spool 106 to the right. The check valve 121 then precludes flow through the line 120 into the chamber 110. The chamber 1 13 at the opposite end of the spool is then filled by fluid flowing into the chamber 113 from the low pressure port 10 via the line 104, ports 124 and 118 and lines 117, 114. The spool continues to move to the right until it reaches the position illustrated in FIG. 5 in which the high pressure port 9 is connected to the third port 11 via line 103, ports 119, 118 ofvalve 102 and lines 117, 116 and 101.

The modification of the third port and valve arrangement illustrated in FIGS. 5 and 6 operates in the same manner as does the transformer heretofore described in connection with the description of the operation of the unit depicted in the FIGS. 3 and 4. Specifically, the third port 11 is connected to the high pressure port 9 when the pump/motor unit 2 or 3 operates as a motor and is connected to the low pressure or case line 120 when the unit 2 or 3 is operated as a pump. This connection occurs automatically so that the volumetric capacity of the unit is reduced as a pump to a value somewhat less than the capacity of the unit as a motor. Consequently, the transformer l depicted in FIGS. 5 and 6 acts in the manner of a large capacity motor driving a smaller capacity pump, irrespective of the direction of power transfer and in spite of the fact that the volumetric capacity of the two units when operating in the same mode is identical.

While I have described only two modifications of my invention, those persons skilled in the arts to which this invention pertains will readily appreciate numerous changes and modifications which may be made without departing from the spirit of my invention. Therefore, I do not intend to be limited except by the scope of the appended claims.

Having described my invention, I claim:

1. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from one of said circuits to the other without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface,

a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces,

a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises a third port entering on at least one of said valve surfaces at a position spaced between said high pressure port and said low pressure port of at least one pump/motor device, and

means including a valve for connecting said third port to said high pressure port of said one pump/motor device when said one pump/motor device is operated as a motor and for disconnecting said third port from said high pressure port and connecting it to a low pressure line when said one pump/motor device is operated as a pump.

2. The transformer of claim 1 in which said low pressure port of said one pump/motor device is angularly longer than said high pressure port of said one pump/motor device and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.

3. The transformer of claim 2 in which said third port of said one piston/motor device is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.

4. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface,

a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces,

a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pres sure port and said low pressure port as said barrels are rotated, the improvement which comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and

means including a valve for connecting each of said third ports to said high pressure ports when said pump/motor device is operated as a motor and for disconnecting said third port from said high pressure port and connecting it to a low pressure line when said pump/motor device is operated as a pump.

5. The transformer of claim 1 in which said low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.

6. The transformer of claim 2 in which said third port of each of said pump/motor devices is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.

7. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluid between the two, which transformer comprises 5 two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface,

a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces,

a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises pressure equalizing means for developing approximately the same pressure on the outlet of that one of the devices which is operating as a pump as is directed into the inlet of the other device to drive the other device as a motor by diverting to a low pressure line a portion of the flow through that device which is acting as a pump.

8. The hydraulic transformer of claim 7 in which said pressure equalizing means comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and means including a valve for connecting each of said third ports to one of said high pressure ports or to a low pressure line, said third port of one device being connected to the high pressure port of the device when the device is operated as a motor and connected to the low pressure line when the device is operated as a pump.

9. The transformer of claim 8 in which said low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.

10. The transformer of claim 9 in which said third port of each of said pump/motor devices is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.

11. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface,

a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces,

a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises pressure equalizing means for developing approximately the same pressure on the outlet of that one of the devices which is operating as a pump as is directed into the inlet of the other device to drive the other device as a motor, said pressure equalizing means being operable to maintain a first rate of flow of fluid into the one device when it is operated as a motor and to maintain a second lesser rate of flow from the device when it is operated as a pump.

12. The hydraulic transformer of claim 11 in which said pressure equalizing means comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and means including a valve for connecting each of said third ports to one of said high pressure ports or to a low pressure line, said third port of one device being connected to the high pressure port of the device when the device is operated as a motor and connected to the low pressure line when the device is operated as a pump.

13. The transformer of claim 12 in which said low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of 

1. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from one of said circuits to the other without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface, a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces, a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises a third port entering on at least one of said valve surfaces at a position spaced between said high pressure port and said low pressure port of at least one pump/motor device, and means including a valve for connecting said third port to said high pressure port of said one pump/motor device when said one pump/motor device is operated as a motor and for disconnecting said third port from said high pressure port and connecting it to a low pressure line when said one pump/motor device is operated as a pump.
 2. The transformer of claim 1 in which said low pressure port of said one pump/motor device is angularly longer than said high pressure port of said one pump/motor device and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.
 3. The transformer of claim 2 in which said third port of said one piston/motor device is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.
 4. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface, a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces, a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and means including a valve for connecting each of said third ports to said high pressure ports when said pump/motor device is operated as a motor and for disconnecting said third port from said high pressure port and connecting it to a low pressure line when said pump/motor device is operated as a pump.
 5. The transformer of claim 1 in which said low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.
 6. The transformer of claim 2 in which said third port of each of said pump/motor devices is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.
 7. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluiD between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface, a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces, a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises pressure equalizing means for developing approximately the same pressure on the outlet of that one of the devices which is operating as a pump as is directed into the inlet of the other device to drive the other device as a motor by diverting to a low pressure line a portion of the flow through that device which is acting as a pump.
 8. The hydraulic transformer of claim 7 in which said pressure equalizing means comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and means including a valve for connecting each of said third ports to one of said high pressure ports or to a low pressure line, said third port of one device being connected to the high pressure port of the device when the device is operated as a motor and connected to the low pressure line when the device is operated as a pump.
 9. The transformer of claim 8 in which said low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.
 10. The transformer of claim 9 in which said third port of each of said pump/motor devices is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port.
 11. A hydraulic transformer for use in combination with two separate hydraulic circuits for transferring power from either one of said two circuits to the other circuit without the flow of any fluid between the two, which transformer comprises two pump/motor devices of the axial piston type, each of said devices having a body including means presenting a valve surface, a high pressure port and a low pressure port spaced therefrom entering on each of said valve surfaces, a rotatable barrel in each of said bodies, said barrels being mechanically interconnected so that they rotate together, said barrels engaging said valve surfaces and containing reciprocal pistons in cylinders defined in said barrels, said cylinders communicating sequentially with said high pressure port and said low pressure port as said barrels are rotated, the improvement which comprises pressure equalizing means for developing approximately the same pressure on the outlet of that one of the devices which is operating as a pump as is directed into the inlet of the other device to drive the other device as a motor, said pressure equalizing means being operable to maintain a first rate of flow of fluid into the one device when it is operated as a motor and to maintain a second lesser rate of flow from the device when it is operated as a pump.
 12. The hydraulic transformer of claim 11 in which said pressure equalizing means comprises a third port entering on each of said valve surfaces at a position spaced between said high pressure port and said low pressure port, and means including a valve for connecting each of said third ports to one of said high pressure ports or to a low pressure line, said third port of one device being connected to the high pressure port of the device when the device is operated as a motor and connected to the low pressure line when the device is operated as a pump.
 13. The transformer of claim 12 in which saId low pressure port of each of said pump/motor devices is angularly longer than said high pressure port and is therefore connectable to said cylinders through a greater angular arc of movement of said barrel than the high pressure port.
 14. The transformer of claim 13 in which said third port of each said pump/motor devices is located approximately equidistantly from one end of said high pressure port and an adjacent end of said low pressure port. 